Immiscibility, nucleation and mechanical properties in the lithia-baria-silica system

Abstract

The current work investigates the effects of nucleation heat treatments, on the microstructure and mechanical properties ofa novel silicate glass in Li2O-BaO-SiO2 system with 1 mol% P2O5 as nucleating agent. As-cast glass was exposed to nucleationheat treatments at 490-550 oC for 1-3 h. The microstructural examination was performed by SEM/EDS. The highest Vickersmicrohardness was determined to be 650 Hv for the sample heat treated at 550 oC for 1 h. The increase in the nucleation timealso affected Vickers microhardness and the highest one was determined to be 600 Hv after nucleation for 3 h. The fracturetoughness, KIC reached 2.51 MPa.m1/2 after nucleation at 550 oC for 1 h. The nucleation temperatures had a more pronouncedeffect on the fracture toughnesses in comparison to nucleation times. The indentation toughness data was used to determineWeibull parameters from Ln ln [1/(1-P)]- lnKIC plots. Weibull modulus, m of the samples nucleated at 500, 510, 530, 550 oCfor 1h. and 540 oC for 2 h. were determined similarly to be 3.8, 3.5, 4.7 and 3.9, respectively. The rest of the samples indicatedhigher Weibull moduli, which may be attributed to the formations of microcracks due to the mismatch in between newlyformed crystals and remaining glassy matrix.